The cellular immunity, particularly cytotoxic T lymphocyte (hereinafter, referred to as “CTL”), plays an important role in the removal of cancer cells or virus-affected cells from living body. CTLs recognize a complex between a peptide fragment of antigen proteins originated from cancer, virus etc. and an MHC class I molecules which is referred to as “HLA” in the case of human, via T-cell receptors, thereby specifically damaging cancer cells or virus-affected cells or activating immune system through the production of various cytokines. A peptide fragment which forms a complex with an MHC class I molecule is referred to as an antigen peptide and is generally about 8-11 amino acids in length. The extracellular domain of an MHC class I molecule consists of α1, α2 and α3 domains, wherein the α1 and α2 domains participate in the formation of peptide binding groove and the α3 domain in the binding with coreceptor CD8 molecule expressed on the surface of CTLS.
Typical examples of tumor antigen protein recognized by CTL comprise those described in Table 1 of Immunity, vol. 10: 281, 1999. Specific examples include melanocyte tissue-specific proteins such as gp100 (J. Exp. Med., 179:1005, 1994) and MART-1 (Proc. Natl. Acad. Sci. USA, 91:3515, 1994), melanosome antigens such as tyrosinase (J. Exp. Med., 178:489, 1993), and, as tumor antigen proteins other than melanomas, tumor markers such as HER2/neu (J. Exp. Med., 181:2109, 1995), CEA (J. Natl. Cancer. Inst., 87: 982, 1995) and PSA (J. Natl. Cancer. Inst., 89: 293, 1997), and SART-1 (J. Exp. Med., 187: 277, 1998) and cyclophilin B (Proc. Natl. Acad. Sci. USA, 88: 1903, 1991) originated from squamous cancer, and the like.
The so-called “cancer vaccine therapy” is considered to be useful in the treatment or prevention of cancer or virus infections, etc., which comprises administering to a subject any of tumor antigen proteins or peptides, or DNAs encoding the same, or virus-originated antigen proteins or peptides so as to enhance specific T cells in vivo. The results of clinical studies conducted with a tumor antigen peptide originated from MAGE-3, which is a tumor antigen protein being overexpressed in melanoma, lung cancer or head and neck cancer, showed significance of vaccine therapy in the tumor rejection (Int. J. Cancer, 80: 219,1999).
In the course of development of agents for vaccine therapy, evaluation/determination of a candidate agent for in vivo usefulness in the vaccine therapy cannot be conducted using pure-line mouse commonly used as experimental animals, and requires transgenic animal expressing HLA (hereinafter, it may be referred to as “animal model for human”). That is, human antigen peptide usable in the vaccine therapy should be such peptide that can induce specific immune response when presented to HLA which is a human-specific MHC class I molecule. Accordingly, non-human experimental animals lacking HLA are unavailable for in vivo evaluation of agents for vaccine therapy directed to treatment of human beings. As mentioned above, transgenic animals expressing HLA (animal models for human) are essential for evaluation of usefulness of agents for vaccine therapy.
Although the construction of transgenic animals is technically understood from various basic textbooks, it is not easy to obtain animals (animal models for human) having desired function. There are many cases where intended animal models could not be obtained; for example, a transgene was poorly or never expressed, a transgenic animal lacked desirable functions as an animal model even if a transgene was expressed, etc. Therefore, the construction and/or establishment of animal models for human is considered to be still an unpredictable technique.
As for animal models for HLA, it is considered to be preferred that, when the animal is mouse, the mouse model for human carries a chimera HLA molecule as a transgene, wherein the α3 domain of HLA gene is replaced by the corresponding domain of mouse MHC class I molecule, and whereby CTLs of animal models can effectively recognize a complex of HLA and antigen peptide. However, there have been no successful examples regarding animal models for human into which a chimera HLA molecule has been introduced except for two reports, i.e., an animal model for HLA-A2.1 (Eur. J. Immunol., 26: 97, 1996; and “HLA-A2.1/Kb transgenic mouse” in J. Exp. Med., 185: 2034, 1997) and an animal model for HLA-A11 (“HLA-A11/Kb transgenic mouse” in J. Immunol., 159:4753, 1997). These publications showed that the presence or absence of CTL induction in response to the administration of an agent for vaccine therapy in transgenic mice highly correlates with that in human, indicating that the transgenic mice are useful as animal models for human.
The above-mentioned HLA-A2.1 and HLA-A11 are HLA haplotypes dominant in Westerners. As a haplotype that is commonly shared by many Asians including 60% of Japanese, HLA-A24 different from these HLAs is well known. If a mouse model carrying a chimera HLA transgene for HLA-A24 is established, it will become possible to conduct in vivo evaluation of HLA-A24 restricted agent for vaccine therapy widely applicable to Asians, which is expected to greatly contribute to the development of pharmaceutical preparations in this field. However, there have been no reports regarding animal models for HLA-A24, and establishment thereof has been demanded. Such animal models are useful in not only evaluation of vaccine preparations but also screening thereof.
The tumor antigen protein PSA is a glycoprotein that is specifically expressed even in normal prostatic epithelial cells and has a blood half-life of 2-3 day. As the canceration progresses, the expression level of PSA increases to give the tumor antigen protein. Accordingly, PSA is used as a marker in diagnosis of cancer, wherein the PSA level in serum of a patient is measured. The prostatic cancer is placed 1st to 3rd place regarding both the incidence and mortality rate among malignant male tumors in many European countries and the United States, and tends to increase in Japan in the late years. As the prostatic cancer is androgen sensitive, treatment is conducted aiming at removal of androgen (endocrine therapy). However, more than half of the cases of prostatic carcinoma progress to recrudescence carcinoma (i.e., androgen refractory carcinoma) in 5 years, even if it responds to and are controlled by endocrine therapy in the beginning of treatment. Such decrease of androgen dependency greatly hampers endocrine therapy of prostatic cancer. Accordingly, the development of vaccine therapy with an antigen peptide of PSA origin is demanded.
An antigenic peptide region of HLA-A2 type has recently been identified in PSA (J. Natl. Cancer. Inst., 89: 293, 1997). However, there have been no reports showing the existence of an HLA type A24 (HLA-A2402)-binding antigen peptide region. Incidentally, many subtypes belonging to MHC class I molecule exist and it is known that there are certain rules (binding motifs) in the amino acid sequence of antigen peptide having a binding ability. In the binding motif for HLA-A24 above, the second amino acid is tyrosine, phenylalanine, methionine or tryptophan, and the C-terminal amino acid is phenylalanine, leucine, isoleucine, tryptophan or methionine. However, peptides identified on the basis of said motif do not necessarily have the immunogenicity. That is, since an antigen peptide is generated through the intracellular processing of a tumor antigen protein, a peptide not having been produced by in vivo processing cannot be an antigen peptide. Furthermore, even if an amino acid region on a tumor antigen protein identified on the basis of the binding motif is intracellularly generated as a peptide, such a tumor antigen protein may be anergic by reason of, for example, it per se exists in a living organism. As described above, a simple prediction based on the binding motif for a given HLA type is insufficient to identify an antigen peptide, and, from this viewpoint, establishment of a mouse model for human which enables to evaluate an HLA-A24-binding antigen peptides has been demanded.